Method for establishing communication path in viscous petroleum-containing formations including tar sand deposits for use in oil recovery operations

ABSTRACT

Many oil recovery techniques for viscous oil recovery such as recovery of bitumen from tar sand deposits, including steam injection and in situ combustion, require establishment of a high permeability interwell fluid flow path in the formation. The method of the present invention comprises forming an initial entry zone into the formation by means such as noncondensible gas sweep or hydraulic fracturing and propping, or utilizing high permeability streaks naturally occurring within the formation, and expanding the zone by injecting steam and a noncondensible gas into the gas swept zone, propped fracture zone or high permeability streak. The mixture of steam and noncondensible gas is injected into the formation at a pressure in pounds per square inch not exceeding numerically the overburden thickness in feet, and the steam-noncondensible gas-bitumen mixture is produced either from the same or a remotely located well. The operation may be repeated through several cycles in order to enlarge the flow channel. Suitable noncondensible gases include nitrogen, air, carbon dioxide, flue gas, exhaust gas, methane, natural gas, ethane, propane, butane and mixtures thereof. Saturated or supersaturated steam may be used.

United States Patent Redford [111 3,908,762 [4 1 Sept. 30, 1975 1 1METHOD FOR ESTABLISHING COMMUNICATION PATH IN VISCOUSPETROLEUM-CONTAINING FORMATIONS INCLUDING TAR SAND DEPOSITS FOR USE INOIL RECOVERY OPERATIONS [75] Inventor: David Arthur Redford, FortSaskatchewan, Canada [73] Assignee: Texaco Exploration Canada Ltd.,

Canada 221 Filed: Sept. 27, 1973 21 App]. No.: 401,529

[521 US. Cl. 166/263; 166/271; 166/272 [51] Int. Cl. EZIB 43/24; E21B43/26 [58] Field of Search 166/272, 271, 263

[56] References Cited UNITED STATES PATENTS 2,910,123 10/1959 Elkins eta1. 166/271 3.208.909 10/1966 Closmann et a1... 166/271 X 3.221.81312/1965 Closmann et a1. 166/271 3.259.186 7/1966 Dietz... 166/2633.279.538 10/1966 Doscher... 166/271 X 3.399.722 9/1968 Buxton et al.166/263 X 3.411.575 11/1968 Connally. Jr.... 166/271 X 3.706.341 12/1972Redford 166/272 X 3.768.559 10/1973 Allen et a1. 166/272 PrimaryE.raminer-Stephen .1. Novosad Attorney, Agent, or Firm-Thomas H. Whaley;Carl G. Ries; Jack H. Park [57] 7 ABSTRACT Many oil recovery techniquesfor viscous oil recovery such as recovery of bitumen from tar sanddeposits.

including steam injection and in situ combustion, re-

quire establishment of a high permeability interwell fluid flow path inthe formation. The method of the present invention comprises forming aninitial entry zone into the formation by means such as noncondensiblegas sweep or hydraulic fracturing and propping, or utilizing highpermeability streaks naturally occurring within the formation, andexpanding the zone by injecting steam and a noncondensible gas into thegas swept zone, propped fracture zone or high permeability streak. Themixture of steam and noncondensible gas is injected into the formationat a pressure in pounds per square inch not exceeding numerically theoverburden thickness in feet. and the steam-noncondensible gas-bitumenmixture is produced either from the same or a remotely located well. Theoperation may be repeated through several cycles in order to enlarge theflow channel. Suitable noncondensible gases include nitrogen, air.carbon dioxide, flue gas, exhaust gas, methane, natural gas, ethane.propane butane and mixtures thereof. Saturated or supersaturated steammay be used.

13 Claims, 3 Drawing Figures US. Patent Sept. 30,1975 Sheet 1 of23,908,762

4 METHOD FOR ESTABLISHING I COMMUNICATION PATH IN viscousPETROLEUM-CONTAINING FORMATIONS INC U I G A A D DEPOSITS FOR USE INOIL'RECOVERY OPERATIONS T1? BACKGROUND-OFTI'IE INVENTION i Fieldoff theInvention l r I t I This invention pertains to'a method forfrecoveringpetroleum from viscous petroleum-containing formations including tarsand deposits and specifically to amethod for establishing a stableinterwell communication path in the formation, and to a'rn'ethodforusing the communication path in an: oilr'ecovery process involvinginjection of a, recovery fluidlsuch as sol-- vent: steam orair for insitu combustion intdtlie communication path ,I i I 2 I y it 'i vDeseriptionjofthe Prior Art L g There are many subterranean,petroleum-containing formations. throughout the' wo rld from whichpetroleum cannot" be recovered -by conventional means because of thehighviscosity of thepetr'oleum contained therein. The best known and mostextreme'exampleof such viscous petroleum-containing" formations are theso-called tar sands or bituminous sand deposits. The largest iand mostfamous such deposit is in' the Athabasca area in the northeastern partofthe Province of Alberta, Canada, which deposit containsin excess of700 billion barrels of petroleum.jOther extensive tar sand depositsexist in thewestern United States and in Venezuela, and lesser depositsare located Europe andAsi a,

Tiaijsah'as are defined as sand saturated with'a highly viscous crudepetroleum material not recoverable in its natural ,state through a wellby ordinary production methods, The petroleum or hydrocarbon/materialscontainedin tar sand deposits are highly bituminousin character, withviscosities ranging in the millions of centipoise at formationtemperature and pressure. The tar sand deposits are about 35 percent byvolume or 83 percent bykwjeight sand, ,and th e sand is generally a finequartzimaterial. The sand grains are coated with alay er of water, andthevoid spacebetwee'n the water coated san d grains isfilledwithbituminous petroleum. Sometar sand deposits have agas saturation,generally air or methane, althougli manyjt ar sand deposits c on- 1 tainessentially no gas The sum of bitumen and waterconcentrationsconsistently equals aboutff/lpercent by weight, with thebitumen, portion thereof varying fr iii about twopercent tofabout" lfipercerit. 'Qne fofthe strikingdifferences between tar sand d'epos its' andmore conventionaljpetroleuni resel voirs isjthela ence ofa consolidatediiji. while the sa'ijiq g'ra' 'ijis aref'iri grainto gra in contact,they: are t not cemented 'togethe f'lhe API gravity ,of ,theg bitumenranges" about 6 'to about 8f,. and the, specific gravit y at60fFahrenheit is from about.l.0 06 toabout 1.021., Y

. Recoyery methods for tar sand deposits arecla's'sifiable as stripmining ,o'rin sit u processesfMostof the recovery. todate, hasbeen bymeans of strip mining, although strip miningiseconomically feasible'atthe'presentrtirnel only in. those deposits wherein jth ratio ofoverburden thickness. toctarhsand depositthicknes's is around 1 o less.lnsitu proi iesseswhich have beenp'rO pqsedi P i rt ha e El e e @PPQI lh. S ti re 'floodin g'. and. .stearn.,injection, as w ie'll as"s te-1 11;- emulsificati on drive processes.

It has' been recognizedin the prior art that many of the thermalprocesses and the 'stea'm emulsification drive process require theestablishmer'it of acommunication pat h'between one or more injectionwells and one or more production wells, through which the re-- coveryfluid maybeinjectedl Many failures to recover appreciable quantities ofbitumen from tar sand deposits by' in situ recovery processes arerelated to plugging ofthe communication path between injection wells andproduction wells. Plugging can occur in a propped frac-' tu're zone asa'result oft'vi/o phenomena. (1) Bitumen" heated by the injected'fluidtoa'sufficiently high temperature wi llflow in the fracture zone for abrief per-' v iold but will lose heat and become so viscous that it isessentially immobile after traveling "only a short distance from thethermal recovery fluid'injection point. (2) When ;a heated fluid such assteam .is injected into a propped fracture communication path betweeninjection and production wells, bitumen above the communication path isheated, softens and flows down into and plugs the'propped fracture zone.

v In view of theforegoing, it can be seen that there is a substantial,unfulfilled need for a method for establishing a stable communicationpath between injection well aha production'wells within a tar sanddeposit, which communication path will not be plugged or otherwiseaffected during the subsequent injection thereinto of a thermal recoveryfluid.

'1 SUMMARY OFTI'IE INVENTION l have discovered, and this constitutesmy'invention, that a stable, permeable communication path may beestablished between wells drilled into'and completed'in a'subterraneanjviscous petroleum-containing formation such as a tar sand depositaccording to the process described belowf'My process requires-that therebe at least moderate gas permeability or a high permeability streakwithin the 'formation, which may be" a naturally occurring highpermeability streak or one which is formed means of conventionalhydraulic fracturing and propping according to techniques well known'inthe prior art. Myp'rocess' utilizes simultaneous injection of s teamand'a noncondensiblegas. The steam' maybe supersaturated or saturated;Gases suitable foruse in my "invention include carbon dioxide,metha'nefnitrog'en,'ai r', and mixturesthereof. 3

through the formation; then gas injection should be the firststep inthis proeess'Any"noncondensible gas such asnitrogen, air, carbondioxide, natural gas or methane may beused. If a permeable streak ispresent-,g'as may be injecte'd'brieflythi'ough'this permeable" streak.Otherwise, hydraulic fracturing and'propping are required to open a zoneinto'which steam and noncond'en'sible gas are injected. Y

"Steam' and the" "no'hondensible gas may be mixed prior-"to injection orinjected sequentially or separately to mix inthe' formation. Theinjection pressure of the 's't e a'rn-rioncondensible gas mixture shouldnot exceed a value in pounds'p'er square 'inchnumerically equal to theoverburdenthicknessin feet in order to avoid fracturing? the overburden;Steam and 'noncondensible gas are injected into one well," and flowthrough the gas ,s'wept zone, permeable streak or propped fracture zoneto a remotely located well. Flow reversal may be used to insure creationo'f'a uniform thickness communication path. Recovery of bituminouspetroleum by more conventional, high efficiency techniques such as steamemulsification drive, combined thermal-solvent injection, or in situcombustion operations may be undertaken next using the communicationpath.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 presents an illustrativeembodiment of my invention, wherein an injection well and productionwell are treated to produce the desired stable commmunication pathaccording to the process of my invention.

FIG. 2 shows the temperature profile of a test cell after 10 minutes ofinjection during evaluation of the process of my invention.

FIG. 3 shows the temperature profile similar to FIG. 2 but after 70minutes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I. The Process My invention maybest be understood by reference to the attached drawings, which shows incross-sectional view, a tar sand deposit type of petroleum formationbeing subjected to one illustrative embodiment of the process of myinvention. In the drawing, tar sand formation l is penetrated by wells 2and 3, which are in fluid communication with the tar sand deposit 1 bymeans of perforations 4 and 5 respectively. Wells 2 and 3 are bothequipped on the surface for injection of fluid thereinto or productionof fluid from the well. This is accomplished by providing well 2 withvalves 6 and 7, and by providing well 3 with valves 8 and 9.

Hydraulic fracturing and propping is performed in the formation via bothwells, which gives rise to the creation of a thin, high permeabilitystreak 10 extending at least part way between wells 2 and 3. Even thoughpropping material is injected into the hydraulic fracture, the fractureis not adequate for sustained injection thereinto of steam in the finalrecovery phase of the operation because of the tendency for heatedbitumen to cool and plug the propped fracture of bitumen above the zoneto flow down into the fracture zone. Accordingly, valve 7 is closed andvalve 6 is opened, and a mixture of steam and noncondensible gas isinjected into well 2 through perforation 4 into the propped fracturezone 10. Noncondensible gas is supplied by a compressor or containedunder pressure in vessel 11 and pumped therefrom by pump 12 into mixingvessel 13. Steam is supplied from generator 14 by a pump 15. Theinjection pressure is raised to the desired value and pumps 12 and 15insure mixing steam and noncondensible gas in the desired ratio. Thematerial being injected into the fracture zone is preferably essentially100% noncondensible gas initially, with the steam content beingincreased with time.

The hydraulic fracturing operation may establish an interwell connectingfracture as shown in the figure, or fracture zones may extend into theformation only part way to the other wells. If an interwell fracturecannot be established, steam and noncondensible gas should be injectedinto each discrete fracture zone via each well. The maximum injectionpressure is still limited by the overburden thickness. The preferredmethod is to inject steam and noncondensible gas up to a pressure inpounds per square inch not greater numerically than the overburdenthickness in feet. Injection of fluid should be stopped and pressureshould then be held at the above described level on all wells for a soakperiod of from 4 to 24 hours. The pressure is then reduced andproduction of steam, noncondensible gas, steam condensate and bitumentaken from all of the wells. This procedure is repeated until interwellcommunication is established.

The presence of noncondensible gas in the fracture zone is thought tohelp avoid formation plugging in several ways. The rate of heating isreduced because the presence of a noncondensible gas with steam reducesthe heat transfer rate significantly. The gas pressure is higher in thefracture zone than it would be if steam alone is present, and thishigher pressure helps hold softened tar sand material in place above thefracture. Moreover, if hot, liquefied bitumen tends to cool and becomeimmobile as its flows through the propped fracture zone and cools, thepresence of noncondensible gas in the zone maintains small flow channelsopen in the immobile bitumen plug through which hot fluids can flow toheat and reliquefy the bitumen plugs. The reason for this effect isrelated'to the high mobility ratio of noncondensible gas and viscousliquid bitumen. Such high mobility'ratio is normally detrimental torecovery efficiency because the high mobility (low viscosity) gas tendsto channel or finger through the viscous petroleum. Channeling in thisinstance is beneficial, since it facilitates passing the hot steamthrough the immobile bitumen, resulting in heating and consequentviscosity reduction of the bitumen. When bitumen becomes immobile andplugs a propped fracture zone such as when steam alone is beinginjected, the portion of the steam vapor near the obstruction cools andeventually condenses, so neither channeling nor heating of the immobilebitumen obstruction results. Injection of additional steam alone is nothelpful since is cannot reach the immobile bitumen obstruction, and theonly heating effect is by conduction along the long dimension, of thefracture, a very inefficient heat transfer process. l

Passage of the mixture of steam and gas through the propped fracturezone results in gradual enlargement of the vertical thickness bycontinually heating bitumen above and below the zone. The viscosity ofbitumen is reduced by heating and flows through the fracture towarcltheproduction well 3, carried along by the flowing steam and gas in proppedfracture zone 10. Although injection of steam would heat and liquefybitumen along the faces of the zone more rapidly than steam andnoncondensible gas, plugging usually results when pure steam is injectedinto a fracture.

Since the heating effect is a function of temperature of the fluidflowing in zone 10, and since the fluid cools as it passes through thezone from injection well to production well, the extent of removal ofbitumen from the formation adjacent to the zone is greatest near theinjection well, decreasing steadily with distance from the point ofinjection. This results in a non-uniform, wedge shaped communicationzone. Although this is not always objectionable, certain recoveryprocesses which may be used give better results if the verticalthickness of the communication path is more nearly uniform. Accordingly,when it is desired to produce a more nearly uniform communication path,the injection-production functions of wells 2 and 3 are reversed, withinjection of steam and noncondensible gas being into well 3 andproduction of steam, steam condensate and liquefied bitumen being takenfrom well 2, this is accomplished using an arrangement such as is shownin the attached figure by closing valves 6 and 9 and opening valves 8and 7 so the mixture of steam and noncondensible gas is introduced intowell 3 and passes therefrom into in terval 10 via perforations 5. Fluidconsisting mainly of steam, noncondensible gas, steam condensate andliquefied bitumen are produced via well 2 through valve 7 to surfacelocated treating facilities.

Whichever injection sequence is being utilized, the fluid produced willbe a mixture of steam, water (steam condensate), bitumen andnoncondensible gas, which must be treated on the surface to separatewater and bitumen. Gravity separation tanks are satisfactory forseparating bitumen and water unless a substantially stable emulsion hasbeen formed due to the presence of naturally occuring emulsifiers in thebitumen. Resolution of water-in-oil emulsions must also be accomplishedand is easily done by contacting the water-in-oil emulsion with an acid.7

Depending on the type of recovery process contemplated in thecommunication path, from one to four or even more repetitive cycles ofthe above treatment may be required to convert the propped fracture zoneinto a satisfactory communication path.

When developing a communication path for an in situ separation processinvolving steam injection, the transition from the communication pathdevelopment phase to the in situ recovery phase can occur smoothly. Thefirst fluid injected into the propped fracture zone will ordinarilyconsist of from 50% to 100% inert gas, the remainder being steam. Afterproduction of inert gas is detected at the production well, the steamfraction of the fluid being injected into the production well isincreased. The maximum safe rate of increase in steam to noncondensiblegas ratio varies from one formation to another because of differences inbitumen composition and content, sand particle size, etc. It isgenerally preferred to inject essentially 100 percent noncondensible gasinitially, and then include gradually increasing quantities of steamwith the noncondensible gas.

One may include a small quantity of an alkalinity agent such as caustic(sodium hydroxide or ammonia) in the first portion ofsteam-noncondensible gas mixture injected to aid in forming ofbitumen-in-water emulsion. Emulsion formation makes possible themovement of bitumen which is otherwise immobile. Removal of bitumen fromthe zone immediately adjacent to the original fracture is necessary inorder to expand the fracture into a communication path which will remainopen upon injection of thermal fluids during the main recovery portionof the process.

The above cycles are continued through a series of separate steps,simultaneously in each well or alternating from one well to the other,until a satisfactory stable, permeable flow path between well 2 and well3 is achieved.

The communication path between wells 2 and 3 established according tothe above procedure may be utilized for a subsequent in situ recoveryprocess such as steam injection, steam plus emulsifying chemicalinjection, or numerous other recovery techniques applicable to tar sanddeposits which required the establishment of an interwell communicationpath. Although steam injected into the communication path via well 2will channel through the communication path, heating of bituminouspetroleum contained in the tar sand deposit will continue along thesurfaces exposed to the communication path through which the heatedfluid is being injected. Bituminous petroleum along the interfacebetween the tar sand deposit and the communication path will be heated,the viscosity will be reduced, and the material will flow into thecommunication path. The bituminous petroleum will then flow toward theproduction well and will be produced along with steam condensate. Therecovery process is aided materially by including a small amount of abasic material such as caustic or sodium hydroxide in the steam, whichenhances the formation of a low viscosity oil-in-water emulsion. Theproduced fluid in such a recovery program is an oil-in-water emulsionwhich has a viscosity only slightly greater than'water. Surfaceequipment for separating bituminous petroleum from the oil-in-wateremulsion must be provided.

The communication path established according to the above describedprocedural steps may also be utilized in the refluxing solvent recoveryprocess described in pending application Ser. No. 357,425, filed May 4,1973.

II. The Noncondensible Gaseous Constituent Gases suitable for use incombination with steam in the process of my invention include carbondioxide, methane, nitrogen and air. Carbon dioxide and methane arepreferred gases because of their high solubility in petroleum, althoughthis solubility must be taken into consideration in selecting the ratioof noncondensible gas, to insure that more than the amount which willdissolve in the petroleum is injected, so some gas-phase will remain atformation conditions. Also, crude gases such as flue gas or engineexhaust gas, both 'rich in carbon dioxide and nitrogen content, may beused. Ethane or propane may also be used. Nitrogen and air are alsopreferred noncondensible gases because of their widespread availability.

llI. Field Example My invention may be better understood by reference tothe following pilot field example, which is offered only as anillustrative embodiment of my invention, and is not intended to belimitative or restrictive thereof.

A tar sand deposit is covered with 300 feet of overburden, and it isdetermined that the thickness of the tar sand deposit is feet. Aninjection and a production well are drilled, 100 feet apart, andcompleted into the full interval of the tar sand deposit. Spinnersurveys indicate that there are no intervals of high permeability withinthis particular segment of the tar sand deposit, and gas permeability ofthe entire formation is quite low. Hydraulic fracturing must beundertaken in order to establish an injection zone for the process of myinvention. Conventional hydraulic fracturing is applied to the formationadjacent to both the injection well and production well, and coarse sandpropping material is injected into the fracture to prevent healingthereof after fracture pressure is removed. Gas injectivity tests areperformed, and it is determined that communica tion between wells hasbeen achieved by fracturing.

Pure nitrogen is injected into the fracutre zone via the injection wellat a pressure of 200 pounds per square inch. After production ofnitrogen from the production well is observed, a mixture of percentquality steam and nitrogen is injected into the well. The volume ratioof nitrogen to steam is initially 1 standard cubic feet per pound, withthe ratio decreasing gradually to about 0.20 over a 6 day period.Approximately 0.2 percent caustic soda (sodium hydroxide) is added tothe steam during the first days of steam injection to aid in forming anemulsion with the bitumen, so that bitumen may be removed moreeffectively from the zone around the fracture more readily. Caustic sodais not needed after 10 days.

Injection of the nitrogen and steam continues for approximately 1 week,which is sufficient to establish a communication path of sufficientextent that pure steam may be injected without danger of pluggingoccurring in the communication path as a result of cooling of bitumen orslumping of heated bitumen into the path. As a safety measure, the steamcontent is increased gradually rather than abruptly, over a 10 dayperiod. Injection of steam is continued as the principal recoverytechnique, bitumen being produced in the form of an oil-in-wateremulsion.

IV. Experimental In order to establish the operability of the process ofmy invention, and further to determine the optimum materials andprocedures, the following laboratory work was performed. A laboratorycell was utilized in these experiments in order to simulate undergroundtar sand deposits. The model is a pipe, inches long and 18 inches indiameter. One inch diameter wells, one for injection and one forproduction, are included, each being positioned three inches from thecell -wall and 180 apart. The top of the well is equipped with a pistonand sealing rings which impose overburden pressure.

The cell described above was packed with a mined tar sand sample andcompressed by pneumatic tamping to a density of 2 gm/cc, followed byapplication of an overburden pressure of 500 psig for 6 days. A 4; inchX 2 inch clean sand path was provided between wells in this sample tosimulate a fracture.

Nitrogen gas flow was adjusted to 24 standard cubic feet per hour at apressure of 300 pounds per square inch into the injection well, throughthe simulated fracture in the compressed tar sand material and out theproduction well, and this was continued for several hours. Steam andnitrogen were injected at a pressure of 300 pounds per square inch. Thefirst production of bitumen occured after only 2 minutes, and thepressure at the models production well quickly rose to above 250F. Therapid occurrence of bitumen production and low pressure differentialbetween the injection and production wells are indicative of formationof a communication path between the injection well and production well.Throughout the run, large amounts of free bitumen (appearance of purebitumen but was actually a water-in-oil emulsion) floated on theoil-inwater emulsion in the production receiver. Steam andnoncondensible gas were injected at a pressure of 290 to 350 pounds persquare inch for 4 5/6 hours, followed by injection of steam only for 2hours before terminating the runJThere was no indication of pluggingduring the run.

Analysis of data obtained from thermocouples placed in the cellindicated a hot flow path across the tar sand between wells and movementof heat outwards from this path. The temperature profile of FIG. 2illustrates this result after 10 minutes of steam injection, and FIG. 3shows the result after 70 minutes of steam injection.

The cell was unpacked in the usual manner and inspected. Major depletionwas noted around the injection port and extending toward the productionport,

with lesser degree of depletion throughout most of the cell.

While my invention has been described in terms of the number ofillustrative embodiments, it should be understood that it is not solimited, since many variations of the process of my invention will beapparent to persons skilled in the related art without departing fromthe true spirit and scope of my invention. Similarly, while a mechanismhas been proposed to explain the benefits resulting from the process ofmy invention, I do not wish to be restricted to any particular mechanismresponsible for the benefits achieved through the use of my process. Itis my desire and intention that my invention be limited only by suchrestrictions and limitations as are imposed in the appended claims.

I claim:

1. In a method of recovering viscous petroleum including bitumen from asubterranean, viscous petroleum-containing formation including a tarsand deposit, said formation being penetrated by at least one injectionwell and by at least one production well, said recovery method being ofthe type wherein a fluid is injected into the injection well for thepurpose of increasing the mobility of the petroleum contained in theformation, the improvement for creating a permeable, stable, fluidcommunication path between the injection well and production well whichcomprises:

a. fracturing the formation adjacent to at least one of the wells byhydraulic fracturing and injecting into the fractured Zone a proppingagent to establish a permeable, propped fracture zone extending at leasta portion of the way into the tar sand deposit toward the other well;

b injecting steam and a gas selected from the group consisting ofmethane, ethane, propane and butane into the propped fractured Zone viathe well adjacent thereto at a preselected pressure; and

c. recovering bitumen, steam and steam condensate from at least one ofsaid wells.

2. A method as recited in claim 1 wherein steam and gas are injectedinto at least one well and travels through the propped fracture to atleast one remotely located well.

3. A method as recited in claim 1 wherein repetitive cycles areperformed with injection alternating between the wells.

4. A method as recited in claim 3 wherein repetitive cycles of injectingsteam and gas and producing fluids from the same wells are continueduntil communication between wells is established.

5. A method as recited in claim 1 wherein steam and gas are injectedinto injection and production wells simultaneously.

6. A method as recited in claim 1 wherein the pressure at which thesteam and gas are injected into the formation is equal to a valuebetween the original formation pressure and a value in pounds per squareinch numerically equal to the thickness of the overburden in feet.

7. A method as recited in claim I wherein the recovery fluid injectedinto the communication path is steam.

8. A method as recited in claim 1 wherein the recovery fluid injectedinto the communication path is a mixture of steam and an alkalinematerial including caustic.

9. In a method of recovering viscous petroleum including bitumen from aviscous petroleun containing formation including a tar sand deposit, theformation being permeable to gas, the formation being penetrated by atleast one injection well and by at least one production well, therecovery method being of the type wherein a fluid is injected into theformation to increase the mobility of the petroleum contained in theformation, the improvement for creating a permeable, stablecommunication path between the injection and production well whichcomprises:

a. introducing a first gas which is noncondensible at formationconditions into the formation via the injection well and recovering thegas from the formation via the production well for a preselected periodof time to create a gas swept zone in the formation;

b. introducing a mixture of steam and a second gas which isnoncondensable at formation conditions into the gas swept zone; and

c. recovering bitumen, steam condensate and the noncondensible gas fromthe production well.

10. A method as recited in claim 9 wherein the first noncondensible gasis selected from the group consisting of nitrogen, carbon dioxide, fluegas, exhaust gas, methane, natural gas, ethane, propane, butane, andmixtures thereof.

11. A method as recited in claim 9 wherein the second noncondensible gasis selected from the group consisting of nitrogen, carbon dioxide, fluegas, exhaust gas, methane, natural gas, ethane, propane, butane,

and mixtures thereof.

12. A method as recited in claim 9 wherein the first noncondensible gasand second noncondensible gas are the same.

13. In a method of recovering viscous petroleum including bitumen from asubterranean, viscous petroleum-containing formation including a tarsand deposit, said formation being penetrated by at least one injectionwell and by at least one production well, said recovery method being ofthe type wherein a fluid is injected into the injection well for thepurpose of increasing the mobility of the petroleum contained in theformation, the improvement for creating a stable, permeable fluidcommunication path between the injection well and production well whichcomprises:

a. hydraulically fracturing and introducing a propping agent into theformation adjacent the injection well and the production well to form apropped fracture zone adjacent each well extending only part way fromthat well to the fracture adjacent the other well;

b. injected steam and a gas-selected from the group consisting ofmethane, ethane, propane and butane into the fracture zone adjacent eachwell until the injection pressure reaches a predetermined value; c.maintaining steam and the gas in each fracture for a predetermined soakperiod; I d. reducing the pressure in each well to permit steam,non-condensible gas and viscous petroleum to flow from each proppedfracture zone into each well.

1. IN A METHOD OF RECOVERING VISCOUS PETROLEUM INCLUDING BITUMEN FROM ASUBTERRIANEAN, VISCOUS PETROLEUM-CONTAINING FORMATION INCLUDING A TARSAND DEPOSIT, SAID FORMATION BEING PENETRATION BY AT LEAST ONE INJECTIONWELL AND BY AT LAST ONE PRODUCTION WELL, SAID RECOVERY METHOD BEING OFTHE TYPE WHEREIN A FLUID INJECTED INTO THE INJECTION WELL FOR THEPURPOSE OF INCREASING THE MOBILITY OF THE PETROLEUM CONTAINED IN THEFORMATION, THE IMPROVEMENT FOR CREATING A PERMEABLE, STABLE, FLUIDCOMMUNICATION PATH BETWEEN THE INJECTION WELL AND PRODUCTION WELL WHICHCOMPRISES, A. FRACTURING TE FORMATION ADJACENT TO AT LEAST ONE OF THEWELLS BY HYDRAULIC FRACTERING AND INJECTING INTO THE FRACTURED ZONE APROPPING AGENT TO ESTABLISHED A PERMEABLE, PROPPED FRACTURE ZONEEXTENDING AT LEAST A PORTION OF THE WAY INTO THE TAR SAND DEPOSIT TOWARDTHE OTHER WELL. B. INJECTING STREAM AND A GAS SELECTED FROM THE GROUPCONSISTING OF METHANE, ETHANE, PROPANE AND BUTANE INTO THE PROPPEDFRACTURED ZONE VIA THE WALL ADJACENT THERETO AT A PRESELECTED PRESSURE.AND C. RECOVERING BITUMEN, STREAM AND STREAM CONDENSATE FROM AT LEASTONE OF SAID WELLS.
 2. A method as recited in claim 1 wherein steam andgas are injected into at least one well and travels through the proppedfracture to at least one remotely located well.
 3. A method as recitedin claim 1 wherein repetitive cycles are performed with injectionalternating between the wells.
 4. A method as recited in claim 3 whereinrepetitive cycles of injecting steam and gas and producing fluids fromthe same wells are continued until communication between wells isestablished.
 5. A method as recited in claim 1 wherein steam and gas areinjected into injection and production wells simultaneously.
 6. A methodas recited in claim 1 wherein the pressure at which the steam and gasare injected into the formation is equal to a value between the originalformation pressure and a value in pounds per square inch numericallyequal to the thickness of the overburden in feet.
 7. A method as recitedin claim 1 wherein the recovery fluid injected into the communicationpath is steam.
 8. A method as recited in claim 1 wherein the recoveryfluid injected into the communication path is a mixture of steam and analkaline material including caustic.
 9. In a method of recoveringviscous petroleum including bitumen from a viscous petroleun containingformation including a tar sand deposit, the formation being permeable togas, the formation being penetrated by at least one injection well andby at least one production well, the recovery method being of the typewherein a fluid is injected into the formation to increase the mobilityof the petroleum contained in the formation, the improvement forcreating a permeable, stable communication path between the injectionand production well which comprises: a. introducing a first gas which isnoncondensible at formation conditions into the formation via theinjection well and recovering the gas from the formation via theproduction well for a preselected period of time to create a gas sweptzone in the formation; b. introducing a mixture of steam and a secondgas which is noncondensable at formation conditions into the gas sweptzone; and c. recovering bitumen, steam condensate and the noncondensiblegas from the production well.
 10. A method as recited in claim 9 whereinthe first noncondensible gas is selected from the group consisting ofnitrogen, carbon dioxide, flue gas, exhaust gas, methane, natural gas,ethane, propane, butane, and mixtures thereof.
 11. A method as recitedin claim 9 wherein the second noncondensible gas is selected from thegroup consisting of nitrogen, carbon dioxide, flue gas, exhaust gas,methane, natural gas, ethane, propane, butane, and mixtures thereof. 12.A method as recited in claim 9 wherein the first noncondensible gas andsecond noncondensible gas are the same.
 13. In a method of recoveringviscous petroleum including bitumen from a subterranean, viscouspetroleum-containing formation including a tar sand deposit, saidformation being penetrated by at least one injection well and by atleast one production well, said recovery method being of the typewherein a fluid is injected into the injection well for the purpose ofincreasing the mobility of the petroleum contained in the formation, theimprovement for creating a stable, permeable fluid communication pathbetween the injection well and production well which comprises: a.hydraulically fracturing and introducing a propping agent into theformation adjacent the injection well and the production well to form apropped fracture zone adjacent each well extending only part way fromthat well to the fracture adjacent the other well; b. injected steam anda gas selected from the group consisting of methane, ethane, propane andbutane into the fracture zone adjacent each well until the injectionpressure reaches a predetermined value; c. maintaining Steam and the gasin each fracture for a predetermined soak period; d. reducing thepressure in each well to permit steam, non-condensible gas and viscouspetroleum to flow from each propped fracture zone into each well.